The present invention relates generally to preparing substrates for electronics, optics or optoelectronics. More specifically, the invention relates to a method for precisely cutting an assembly formed of two layers of material that has two principal surfaces. The method includes providing a weakened interface between the two layers, wherein the interface defines an interface ring at the periphery of the assembly. A first high-pressure zone is provided whose border includes at least one part of the interface ring, and at least one second low-pressure zone is formed whose pressure is controlled relative to one part at least of a principal surface of the assembly. The high-pressure zone is supplied with a fluid, whose pressure is controlled.
For the purposes of this text, the term “cutting” is understood to mean the operation of dividing a single element or assembly into two physically separate parts wherein the parts do not combine again.
Methods for cutting two layers of material of an assembly are well-known, for example, as disclosed in International Application No. WO 01/04933. That document also describes a device for implementing the method. In particular, this document describes the production of at least one cavity in the interface zone, the cavity then being used for initiating the cutting of the two layers defined by the interface. A limitation of the disclosure of this document is that it only enables cutting of layers that have been previously bonded together, so that the weakened interface is necessarily a bonding interface. It would be advantageous to be able to implement a method of this type for cutting layers separated by any type of weakened interface. It would thus be advantageous to be able to implement a method of the aforesaid type, for example, for cutting layers separated by a weakened interface that has been defined by implantation of elements such as ions or atoms in a substrate of material (the two layers being thus produced using the same material).
One way of defining a weakened interface in a substrate of the type used for electronics, optics, or optoelectronics includes implanting elements such as hydrogen ions in the substrate mass using a controlled implantation energy to precisely define the depth of implantation of the elements. One such substrate (called a ‘wafer’ according to the generally accepted terminology) can be, for instance, a semiconductor material such as silicon.
It is also possible to produce a weakened interface by using any other known method, for example, by constructing an intermediate zone of porous material between two zones of dense material. For example, by using a layer of oxide embedded in a substrate (a silicon-on-insulator (SOI) type substrate, for example). The bonding of the two layers is thus only one particular way of creating a weakened interface between two layers.
The present invention seeks to implement a method of the aforesaid type for cutting an assembly at a weakened interface that has been formed by one of the hereinbefore described means, or by any other known method.
It is noted that that other methods are known that enable cutting of layers separated by a weakened interface created by implantation of atomic particles. An example of one such method can be found in U.S. Pat. No. 6,221,740. But that method does not provide the specific advantages of the type of method described in International Application No. WO 01/04933. In particular, the method does not teach how to precisely control the pressure in the two different zones (corresponding to the high-pressure zone and the low-pressure zone mentioned above). Such control is important for performing the cutting operations with precision and for avoiding the risks of degrading the wafers, which are fragile and which are expected to have an extremely high surface quality after cutting. The device described in U.S. Pat. No. 6,221,740 thus does not enable one to control the pressure in one single zone of high pressure, which is adjacent to at least one part of the interface ring. And it must be noted that even this control cannot be carried out in a precise manner due to the significant risk of leakage at the interface ring (a certain tightness being provided by an O-ring seal positioned relative to the interface ring), although as stated in U.S. Pat. No. 6,221,740 (see col. 4, lines 21-22 and lines 34-36) this tightness is relative.
Furthermore, U.S. Pat. No. 6,221,740 does not have the advantageous structure type described in International Application No. WO 01/04933, which not only enables defining at least one high-pressure zone and one low-pressure zone in which the pressure can be precisely controlled, but moreover enables the assembly to be cut to deform freely when being cut (namely owing to the absence of contact on a significant portion of the principal surfaces of the assembly). Thus, the structures of the devices of International Application No. WO 01/04933 and U.S. Pat. No. 6,221,740 exhibit fundamental differences that correspond to fundamental functional differences.
It would thus be advantageous to preserve the advantages of the method of International Application No. WO 01/04933 (including controlling both the high and low pressure to precisely control the loads applied to the assembly as well as generally allowing the assembly to deform freely during cutting), wherein these advantages are absent in the configuration described by U.S. Pat. No. 6,221,740. It would also be beneficial to enable efficient cutting at a weakened interface that would be produced by any means (by implantation, for example), which is not suggested in the method and device of International Application No. WO 01/04933, which is strictly limited to cutting a weakened interface corresponding to a bonding interface.